Marijuana is the most commomly used illicit drug in this country. Cannabis use is associated with significant cognitive and emotional deficits. Marijuana alters the function of the noradrenergic locus coeruleus (LC), a brain region that mediates stress, pain, anxiety, arousal and attention. This region is adversely affected by cannabinoid exposure, and these adverse effects appear to be modulated by the interaction of cannabinoid (CB1) and opioid (MOR) receptors within the LC. This project proposes to elucidate the cellular mechanisms of cannabinoid modulation of MOR in the LC. By doing so, it will be possible to better understand the role of cannabinoids in LC-mediated pain modulation and stress/anxiety- related dysfunction. The mechanism of cannabinoid-opioid interaction in the LC will be studied from several different perspectives. Cannabinoid modulation of MOR will be examined at the level of receptor regulation through Western blot analysis and in situ hybridization. The anatomical substrates of CB1-MOR cross-talk will be explored using electron microscopy to determine ultrastructural localization and receptor trafficking patterns. Finally, the components of signaling complexes will be analyzed to determine the mode of cannabinoid- opioid interaction at the level of convergent signal transduction pathways. The implications of cannabinoid use for LC function will be best elucidated using this multifaceted approach. The research outlined in this proposal will more clearly define the risks and potential benefits associated with cannabinoid-opioid interactions. Relevance of this research to public health: The prevalence of marijuana use in this country is a serious public health problem. It is essential to understand the changes that occur in the brain as a result of marijuana use. Alterations in a brain region called the locus coeruleus may be related to the anxiety and stress-related dysfunction resulting from regular marijuana use. Cannabinoids may also influence the way pain signaling is processed by the locus coeruleus, revealing a potential new target for pain therapeutics.